I figured something out, today. Oddly enough, this revelation occurred during my morning swim (1.2 miles worth, to provide some comparison for TriGreyhound). What I figured out is one of the things that makes swimming so much more challenging than biking and running.
We all know that running is an extremely demanding activity. It burns significant energy. It gives the body a good pounding. Varying weather conditions have a huge impact on our heating and cooling system. It's tough, but I consider it a great deal easier than swimming.
Biking is also a demanding sport. While less abusive (discounting any crashes) than running, it still requires amazing leg strength. Maintaining proper form for such a long time is challenging, even with a proper fit. And we won't even talk about what a pain in the butt (literally) biking can be. Even so, it is also a great deal easier than swimming.
Swimming takes place in a relatively cool medium. It is generally less demanding in an aerobic sense. And it uses muscles that aren't beat up from other disciplines. Even after vast improvements in form and getting a better grasp on breathing, swimming is still the most "demanding" aspect of the sport of triathlon (from my perspective).
Today, I figured out why. It's all in the mental "freedom" that exists in each discipline. I accomplish a great deal of contemplation while running and biking. The activities are so second nature that my mind is free to wander over a broad range of topics. I do complex math calculating pace and distance. I plan sermons for when my pastor is out of town. I just spend a lot of time thinking about anything except what I'm actually doing. It makes long runs and rides pass more quickly.
When I'm swimming, all of my thoughts and focus are on swimming. Arm form, breathing technique, when to actually breathe, laps completed, body alignment, etc. All of my mental energy is focused on managing to actually NOT drown. If my mind begins to wander to other things, my form goes to pot, I start to breath water, and I slow down. Then, my mind snaps back to swimming, and it gets better.
That is what makes swimming the most burdensome portion of triathlon. The question is one of muscle memory. As I spend more time swimming, will the proper form become as second nature as running or biking? I sure hope so. But somehow, I imagine the need to breathe air will continue to dominate my thinking.